Manufacture of seamless pipes



June is, 1936. K KORBULY 2,044,358

MANUFACTURE OF SEAMLESS PIPES Filed Oct. 12, 1934 Patented June 16, 1936 umrso s'rArEs.

PATENT OFFlQE MANUFACTURE or ssamass runs Karoly Korbuly, Csepel," Hungary, assigno'r to Alfina Immobllien-Finanzierungs & Verwaltungs A. G., Glarus, Switzerland Application October-12,1934, Serial No. mm In Hungary January 3, 1934 Claims. (01. 80-11) ing in a single heating, the strain exerted on the workpiece at the point of engagement of the thrust mandrel is still of such magnitude that a tearing of the workpiece occurs Therefore, it has been proposed to' drive positively the small rolls of the passes in a similar manner to that usual in rolling mills, the rolls of which have such a large diameter that they can bite on and drawn in the workpiece with the mandrel even without positively forwarding the latter. If the hollow blank is to be drawn in a single heating down to the usual wall thickness of a gas pipe, say, to about 2.5 mm. and less, substantial constructional difllculties would be caused by the positive driving of the pass rolls owing to their large number.

The individual roll passes with positively driven rolls would occupy a comparatively large length,

so that with the large number of passes necessary for drawing down\the blank to the wall thickness of gas pipes the total overall length resulting for the thrust bench would be too large for practical purposes and would allow in any case me workpiece to cool below the drawing temperature before reaching the last pass.

The positive driving of the rolls of the drawing puses can be, however, avoided it according to 3 the invention the forwarding of the workpiece effected by means of the mandrel is assisted by one or more advancing roller passes with positively driven rollers of a sufllciently large diameter to bite on and draw in the workpiece, and which are inserted in the series oil-loose roll drawing passes.

According to a feature of the invention, in addition to or instead of the positively driven ad vancing roller passes, after or between a series of loose roll reducing pases with rolls having a trough diameter less than twice the pass diameter, friction passes are inserted consisting of rloose rollers having a trough diameterwhich is greater than that of the rollers of the reducing passes. Fig. 1 of the drawing shows a diagrammatic longitudinal section of an example of an arrangement of the loose roll drawing passes and the positively driven advancing pass rollers.

'Fig. 2 shows a front view of a loose roll drawing pass.

- Fig.3 shows an arrangement with no positively driven advancing rollers atall. I

The hollow incandescent pipe blank i closed at one end is placed in the usual manner ,on the mandrel 2, which is forwarded in the direction of 5 the arrow by means of the known thrusting or pulling device of thrust or drawing benches in order to force the workpiece together with the mandrel through the drawing passes 5(b-5d consisting of loose rolls 6, Fig. 2. 10

In addition to the passes 5ll-5d with loose rolls 6, which do the main part of drawing, there are provided according to the invention roller passes la and 1b, which consist of positively driven rollers and by biting on the workpiece and drawing it in, 15

assist the forwarding of the workpiece performed by the mandrel 2. The loose roll drawing passes,

which do not advance the workpiece, but cause only a reduction of its wall thickness and the stretching of the workpiece forwarded by the 20 mandrel, must set up as low frictional resistance against the advancing of the workpiece as possible. For this reason the smallest diameter of the loose rolls 6 viz. its diameter on thebottom of groove, that is to say its trough diameter, must 25 it wlllbe substantially smaller than that one of the much smaller loose pass rolls. I

For this reason (owing to their advancing action prepondering over their stretching action) the positively driven larger rollers will be termed advancing rollers, while in contradistinction thereto the smaller loose rolls causing only stretching, will be termed drawing rolls".

The individual drawing passes may consist of two or more loose rolls, for instance, as, shown in Fig. 2, of three loose rolls. Each advancing roll- 45 er pass Ia-lb may consist either of a couple or of a plurality of rollers. It is necessary to insert at least one positively driven advancing roller pass, for instance, the pass lb, in the me of loose roll passes, "so that at 1e t one positively driven advancing roller pass I is preceded by a file of loose roll'drawing passes to, 5b, or files of loose roll drawing passes 5a, 5b or 50, 5d may alternate withpositively driven advancing roller-passes inserted therebetween. A positively driven advancing roller pass la could also be arranged in front of the first loose roll drawing pass.

- may be avoided as will be understood on the following consideration.

The roll passes must allow in each pass the highest possible degree of stretching with the lowest possible frictional resistance, for which reason the rolls must have the smallest possible diameter which is preferably of the order of magnitude of the calibre diameter, in any case less than twice the calibre diameter. An increase in the diameter of .the pass rollsresults in an increase of the friction arising in the pass and in a reduction of the limit of stretching obtainable therein, until with a sufficiently large increase of the roll diameter, the friction becomes so great that if the rolls are positively driven, the latter can draw in and advance the workpiece even if the advance is not produced by means of the mandrel. To this end it will be necessary in practice to employ rolls, the diameter of which amounts to a multiple of the diameter of the calibre, in any case more than four times this diameter. The invention makes use of this fact in this manner that, in addition to the loose roll passes effecting the highest possible degree of stretching with a small amount of friction, the rolls of which passes therefore receive the smallest possible trough diameter (not more than twice thecalibre diameter) and termed stretching roll passes, there are arranged between or following the stretching roll passes, a plurality of passes consisting too of loose rollers. having, however, a larger trough diameter than those of the stretching passes. Owing to the high friction arising in these latter passes and their comparatively small stretching action. these latter passes are to be termed friction roll passes. 0n forcing the workpiece advanced by the mandrel through the friction roll passes comparatively high squeezing forces act on the workpiece therein, which squeeze it against the mandrel, whereby large frictional forces arise between the workpiece and the mandrel which are directed in an opposite sense to the advancing movement and also to the tensile stress produced in the workpiece by the thrust of the mandrel so that the tearing strain is reduced by said frictional forces. The: trough diameter of the rollers of the friction passes is preferably smaller than that which would benecessary if passes 8b may be inserted between the stretching passes of the file.

The sliding friction arising in the stretching passes can be still further reduced by the rollers of the friction passes touching the workpiece at a longer are than the rolls of the stretching passes. This could be effected by using rolls in the stretching passes with a larger radius of curvature in their axial section, than'ithe' radius of the cross-section of the workpiece, which would give more or less open passes. Preferably, however, closed passes are employed for the friction and stretching passes but the friction passes are composed of a smaller number of rolls than the stretching passes. Thus, for instance, it is preferable to use as friction pass, a couple of rollers forming a closed calibre between them, while three or more rolls are combined into a closed calibre for the stretching passes.

What I claim is:--

l. The method of manufacturing seamless pipes, comprising forcing a mandrel-carried pipe blank through a series of reducing passes including loose rolls with an insufficient diameter.

for drawing in the workpiece when same is positively driven, forcing the workpiece by means of the advanced mandrel, and assisting the mandrel by at least one positively driven advancing roller-pass in the series of loose roll passes, said pass biting on the,workpiece due to its having a diameter sufliciently large for drawing in the workpiece.

2. In a device for the manufacture of seamless pipes and including positively driven advancing rollers, a series of loose roll reducing passes with rolls having a. trough diameter less than twice the pass diameter, friction passes composed of loose rollers having a trough diameter greater than the trough diameter of the rolls of the reducing passes, and arranged in operative relation with said reducing passes.

3. .In a drawing bench including a forwarding device for a mandrel and with loose roll passes; positively driven advancing roller passes and a series of loose roll passes, the former being inserted in the series of loose roll reducing passes, the trough diameter of the advancing pass rollers being greater than that of the loose reducing pass'rolls.

4. In a device for making seamless pipe, positively driven advancing rollers, a series of loose roll reducing passes with rolls having a trough diameter less than twice the pass diameter, and, arranged in operative relation therewith, friction passes composed of loose rollers having a trough diameter greater than the trough diameter of the rolls of the reducing passes, the

friction passes having a smaller number of rollers than the reducing passes.

' 5. In a device for making seamless pipe, positivel'y driven adyancing rollers, aseries of loose roll reducing passes with rolls having a trough diameter less than twice the pass diameter, and,

arranged in operative relation therewith, friction passes composed of loose rollers having a trough diameter greater than the'tro'ugh diameter of the rolls of the reducing passes, the friction passes being formed as closed passes and com-- prising'a smaller number of rollers than the re- To 

